dB or Not dB?

One of the most confusing topics for my General Class students is the dB. I can understand why they’re confused. First of all, it’s an expression of a ratio, not an absolute unit. Second, it’s logarithmic, not linear. Third, there are a number of different units that are called dB: dB, dBm, dBV, etc.

AudioDesignLine.Com has started a series of articles excerpted from the book, Sound System Engineering, that attempts to the explain the decibel. The first article in the series is “Using the Decibel – Part 1: Introduction and underlying concepts.” It starts out with an interesting history of how engineers in the 1920s at Bell Labs came up with the concept of the decibel. What they were trying to do is to describe signal losses in telephone circuits.

Fortunately, for engineers–and amateur radio operators–the concept of the decibel can be applied to RF circuits and antennas, as well as telephone and audio circuits. Mastering the concept can really help you envision what’s going on in these circuits and systems.

FCC’s Bill Cross, W3TN, Call Ham Radio “Below the Radar”

From today’s ARRL Letter:

William Cross, W3TN, a staff member in the FCC’s Wireless Telecommunications Bureau, and Riley Hollingsworth, Special Counsel for the Spectrum Enforcement Division of the FCC’s Enforcement Bureau, spoke at the FCC Forum on Saturday afternoon at the 2008 Dayton Hamvention. Cross opened by explaining just where Amateur Radio falls in the FCC’s bureaucracy.

“The Mobility Division of Wireless Telecommunications Bureau has the oversight of the Amateur Radio Service,” Cross said. “We handle the day-to-day administration of the Amateur Service and some of the rulemaking activities that affect the Amateur Radio Service. The Gettysburg office handles applications, licensing — including vanity calls — and the ULS. Within the Commission, other bureaus also make rules that affect you. The Office of Engineering and Technology handles spectrum allocations and equipment issues. Our Managing Director’s Office is the office that handles matters relating to fees, such as the fees relating to vanity call signs, Debt Collection Improvement Act matters, the need for Federal Registration Numbers.”

Cross divided comments into two areas: Proceedings where the Commission has issued a decision and rulemaking requests that have been filed with the FCC, but which are pending resolution by the Commission.

Calling the past year “interesting, because it has been a quiet year on the regulatory front,” he said that no big rulemaking items were released. “This being an election year, there doesn’t seem to be any legislation on Capitol Hill that is of direct interest or impact on the Amateur Service. This year is a good time for Amateur Radio to be flying ‘below the radar,’ and that’s where ham radio is right now in terms of the big picture — below the radar,” Cross said. “We wrapped up a couple of Petitions for Rulemaking [PRM] that were pending and it doesn’t look like (at least in the near future) there will be anything else coming out.”

One of the cases the FCC issued a decision on was what Cross referred to as the Miller Order. This Order, released May 7, dismissed a PRM from Mark Miller, N5RFX. Miller sought three points: To delete the FCC’s 2006 addition to how it defines data, to amend the rules to prohibit automatically controlled stations from transmitting on frequency segments other than those specified in Section 97.221(b), and to replace the symbol rate limits in Section 97.307(f) with bandwidth limitations.

“The effect of these changes,” Cross explained, “when taken together, would have been, as [Miller] said, ‘A small number of wider bandwidth modes, including Pactor III, would no longer be authorized.’ Translating that into English, what he was asking for was ‘bye-bye Winlink.’ Don’t get me wrong — Winlink as a communications system seems to have become the ‘Brussels sprouts of ham radio’ — you either love it or you hate it. And trying to bury it under ketchup or hollandaise sauce hasn’t changed the basic like or dislike for Winlink. Most of the controversy here seems to swirl around how certain licensees use it. Some use it for a radio e-mail system. Others use it for getting weather maps while they are on sailboats in places the brave dare not go. Others use it for their personal business activities, such as buying and selling stocks. These uses are really a Section 97.113, a ‘prohibited communications’ question, not a technology question.”

Cross mentioned that there are “some things coming down the pike that you want to keep track of. The ARRL has a pending petition — RM 11325 — that requests that we amend the rules that apply to the power stations may use when transmitting spread-spectrum emissions — BPL. The DC Circuit Court of Appeals remanded the FCC’s final BPL rules. The Court did not vacate the rules, so they are still in effect. There will be another proceeding to address what the Court told the Commission it had to address.”

The Northern California Packet Association has filed a request for clarification that the FCC define what is meant by the term “simultaneously” as it is used when defining a repeater. “The issue here is that in California,” Cross explained, “D-STAR repeaters have been coordinated on channels that are set aside for auxiliary stations, on the basis that, because there is a delay in retransmission of the signal, the retransmission is not simultaneous, and therefore the repeating station is not a repeater.” Cross said others have advanced what he calls “the duck argument: If the station looks like a repeater, if it functions like a repeater, and it sounds like a repeater, it should be treated as a repeater — and confined to the repeater subbands. A decision on this will be coming [from the Commission] shortly.”

When Hollingsworth stepped up to the podium, he spoke about what he called “the magic of radio,” saying, “we need to realize the debt we owe to those who work so hard to further the goals of Amateur Radio, whether it’s the Emergency Communications participants, club members, teachers, VEs, the League. One of the richest rewards in doing something is to experience joy in doing it. And with so many people working so hard on their own time to further the goals of Amateur Radio, we’re all a little more free to enjoy radio and to make it fun as well as a public service.”

Saying that “things have calmed down a lot in the Amateur Radio Service,” Hollingsworth explained, “[that] when it comes to the Amateur Radio Service, there’s one enforcement tool we need very badly and we just don’t have it — and that’s straitjackets,” he deadpanned, eliciting guffaws from the crowd of more than 150 people. “Some days I want to ask, ‘Why can’t everybody just get along?’”

Hollingsworth noted that since the 75 and 80 meter phone band has been expanded, “a lot of these regular small groups, ragchews and some of the Nets should consider “spreading out, because a lot of the regular operations every night are clumped together. Yes, there are still interference issues and interference allegations, but if everybody would spread out a little bit, now, it’s going to take a real change of habit by a group that has used the same frequency for 40 years to talk across the state, but you really need to spread out and take advantage [of the band] expansion.”

He also noted that interest in Morse code “seems to be higher than ever before.” On the enforcement side, Hollingsworth said he has noticed “no difference in enforcement problems related to no-code, and I think I’m seeing more young people at events that I go to.” He reminded audience that only 1 percent of Amateur Radio licensees filed comments in the Morse code Proceeding. “I see the new code keys for sale here, and I always see a big crowd of people around anything related to code or code keyers. I think the interest has really peaked.”

Hollingsworth pointed out a 12 year old boy who sat in the front row. When asked, the boy responded he received his license three years ago when he was 9. “The future President of the League might be sitting right there,” Hollingsworth explained, pointing at the boy. “That’s our future, right there, and we’re depending on you. We need a lot more young people and I think that Morse code seems to interest young people — hopefully they’re getting tired of instant messengers and the Internet. Last night someone told me about a 14 year old Net Control Operator on a national Net.”

Calling for “more courtesy” on the Amateur Radio bands, Hollingsworth said, “This fighting amongst yourselves is the worst thing that you can do. You have some rude operators and operators who don’t care and who are hateful and bitter about life in general, but every group has that, whether it’s doctors, electricians, lawyers, plumbers, whatever, every group has a certain percentage of people like that. What you have to do is to remind yourself every day to stay on the high road and report to us if you can’t resolve a problem after you’ve given it a chance to go away. There are plenty of ugly situations in the world and you don’t have to add to them. Now, there are a few idiots in your Service who know all the answers, only because they haven’t thought of all the questions. They just want recognition and reaction. Don’t give it to them. Don’t be baited. Don’t feel insulted — they are their own worst punishment. Don’t dignify them with a response.”

Hollingsworth implored the audience to “never let the Commission get by again with handing you 10 to 12 years of neglect. You have to stay vigilant. Even though the bands may sound better to you, you have to be vigilant to protect your Service, and be part of the solution — not the problem — and operate as if the whole world is listening, because generally it is.”

You can listen to the FCC Forum in its entirety on the ARRL Web site.

RF Trends Webinar: Wednesday, May 28, 2008

This webinar is being presented by the Institute of Electrical and Electronics Engineers (IEEE). I am a member, but it looks like you can sign up even if you’re not an IEEE member. Here’s the info:

2:00 PM ET / 11:00 AM PT / 18:00 GMT (Duration: 1 hour)

This presentation will cover the wireless landscape—from challenges to solutions—including the most recent developments in cognitive radio platforms. Market demand is driving devices to support new and emerging combinations of spectrum bands and modulation schemes. How are designers responding to this increasing complexity? What are the technology drivers and challenges in meeting RF test and software requirements? How are device manufacturers and chipset suppliers addressing these challenges, and what can we expect from the next level in wireless performance.

You will also learn about recent development in cognitive radio technology with a discussion of the conflicting requirements of speed and flexibility for processing multilayer IP-based communication protocols. This Webinar will contrast the fundamentally different processing requirements of network-centric multimedia communication protocols to the computer-oriented applications targeted by general-purpose and embedded DSP CPUs, and will delve into current developments outside the realm of a software-defined radio framework.

Click here to register.

From NIST Tech Beat, May 13, 2008

Here are a couple of items from the NIST Tech Beat, an e-mail newsletter of the National Institute of Science and Technology. The first could really be important in an emergency situation. The second is still more in the realm of research, but the speed at which some of these things become products, I wouldn’t be surprised if we soon see products based on this technology.

Emergency Links: NIST Identifies ‘Sweet Spot’ for Radios in Tunnels

As part of a project to improve wireless communications for emergency responders, researchers at the National Institute of Standards and Technology (NIST) have confirmed that underground tunnels—generally a difficult setting for radios—can have a frequency “sweet spot” at which signals may travel several times farther than at other frequencies. The finding, which uses extensive new data to confirm models developed in the 1970s, may point to strategies for enhancing rescue communications in subways and mines.

The optimal frequency depends on the dimensions of the tunnel. For a typical subway-sized tunnel, the sweet spot is found in the frequency range 400 megahertz (MHz) to 1 gigahertz (GHz). This effect is described in one of two new NIST publications.* The reports are part of a NIST series contributing to the first comprehensive public data collection on radio transmissions in large buildings and structures. Historically, companies have designed radios based on proprietary tests. The NIST data will support the development of open standards for design of optimal systems, especially for emergency responders.

NIST researchers were surprised by how much farther signals at the optimal frequency traveled in above-ground building corridors, as well as underground. Tunnels can channel radio signals in the right frequency range because they act like giant waveguides, the pipelike channels that confine and direct microwaves on integrated circuit wafers, and in antenna feed systems and optical fibers. The channel shape reduces the losses caused when signals are absorbed or scattered by structural features. The waveguide effect depends on a tunnel’s width, height, surface material and roughness, and the flatness of the floor as well as the signal frequency. NIST authors found good agreement between their measured data and theoretical models, leading to the conclusion that the waveguide effect plays a significant role in radio transmissions in tunnels.

Lead author Kate Remley notes that the results may help design wireless systems that improve control of, for example, search and rescue robots in subways. Some handheld radios used by emergency responders for voice communications already operate within the optimal range for a typical subway, between around 400 MHz and 800 MHz. To provide the broadband data transfer capability desired for search and rescue with video (a bandwidth of at least 1 MHz), a regulatory change would be needed, Remley says.

The tunnel studies were performed in 2007 at Black Diamond Mines Regional Park near Antioch, Calif., an old complex used in the early 1900s to extract pure sand for glass production.

The second new NIST report** describes mapping of radio signals in 12 large building structures including an apartment complex, a hotel, office buildings, a sports stadium and a shopping mall.

The research is supported in part by the U.S. Department of Justice and the Department of Homeland Security. Both reports will be available on NIST’s Metrology for Wireless Systems Web page.

* K. A. Remley, G. Koepke, C. L. Holloway, C. Grosvenor, D.G. Camell, J. Ladbury, R.T. Johnk, D. Novotny, W.F. Young, G. Hough, M.D. McKinley, Y. Becquet and J. Korsnes. “Measurements to Support Modulated-Signal Radio Transmissions for the Public-Safety Sector”. NIST Technical Note 1546, April, 2008.

** C. L. Holloway, W.F. Young, G. H. Koepke, K. A. Remley, D. G. Camell and Y. Becquet. “Attenuation of Radio Wave Signals Into Twelve Large Building Structures”. NIST Technical Note 1545.

Disorder Enables Extreme Sensitivity in Piezoelectric Materials

A research team working at the National Institute of Standards and Technology (NIST) has found an explanation for the extreme sensitivity to mechanical pressure or voltage of a special class of solid materials called relaxors.* The ability to control and tailor this sensitivity would allow industry to enhance a range of devices used in medical ultrasound imaging, loudspeakers, sonar and computer hard drives.

Relaxors are piezoelectrics—they change shape when a battery is connected across opposite ends of the material, or they produce a voltage when squeezed. “Relaxors are roughly 10 times more sensitive than any other known piezoelectric,” explains NIST researcher Peter Gehring. They are extremely useful for device applications because they can convert between electrical and mechanical forms of energy with little energy loss.

A team of scientists from Brookhaven National Laboratory, Stony Brook University, Johns Hopkins University and NIST used the neutron scattering facilities at the NIST Center for Neutron Research (NCNR) to study how the atomic “acoustic vibrations,” which are essentially sound waves, inside relaxors respond to an applied voltage. They found that an intrinsic disorder in the chemical structure of the relaxor crystal apparently is responsible for its special properties.

Atoms in solids are usually arranged in a perfect crystal lattice, and they vibrate about these positions and propagate energy in the form of sound waves. In typical piezoelectric materials, these acoustic vibrations persist for a long time much like the ripples in a pond of water long after a pebble has been thrown in.

Not so with relaxors: these vibrations quickly die out. The research team led by Brookhaven’s Guangyong Xu, compared how the sound waves propagated in different directions, and observed a large asymmetry in the response of the relaxor lattice when subjected to an applied voltage.

“We learned that the lattice’s intrinsic chemical disorder affects the basic behavior and organization of the materials,” says Gehring. The disorder that breaks up the acoustic vibrations makes the material structurally unstable and very sensitive to applied pressure or an applied voltage.

That disorder occurs because the well-defined lattice of atoms alternates randomly between one of three of its elements—zinc, niobium and titanium—each of which carries a different electrical charge.

The research was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy’s Office of Science and the Natural Science and Research Council of Canada.

* G. Xu, J. Wen, C. Stock and P.M. Gehring. Phase instability induced by polar nanoregions in a relaxor ferroelectric system. Nature Materials. Published online May 11, 2008.

Why Can’t Dayton Be More Like the Maker Faire?

I got this via e-mail yesterday:

If You MAKE It, They Will Come–O’Reilly Media Alert:
Maker Faire attracts an incredible 65,000 attendees

Sebastopol, CA—Earlier this month, an astonishing 65,000 people from all across the country (and beyond) came to the San Francisco Bay Area to celebrate the world’s premier event for DIY (Do It Yourself) creativity—Maker Faire! Organized by Make Magazine and Craft Magazine, Maker Faire celebrates things people create themselves—from electronic gizmos that would make James Bond jealous, to “slow made” foods and homemade clothes that would make Martha Stewart swoon.

The next Maker Faire will take place October 18 & 19 at the Travis County Fairgrounds in Austin, TX. In 2009, Maker Faire may expand to even more locations. “Makers are everywhere, in every city across America and the world,” explained Dale Dougherty, founder of Maker Faire. “We want to tap into these communities, to showcase what people are making, and, in the end, to encourage and inspire even more people to become Makers.”

While still the ultimate playground for hackers and geeks, Maker Faire is bringing the inventive and fascinating world of DIY into the mainstream. “We’re amazed at how fast this has grown,” said Event Director Sherry Huss. “Maker Faire has clearly struck a nerve in American culture. We’re reaching 7 year olds, 70 year olds, and everyone in between.”

The figure of 65,000 attendees especially resonated with me as I just got back from attending Dayton, where attendance was down and the number of vendors—both outside and inside—was down. We can all blame it on the economy and gas prices, but if these guys can attract 65,000 people under the same conditions, I don’t think that argument holds much water.

What is it then? One thing that comes to mind is moving the Hamvention somewhere cooler, say Austin, TX. Being a long-time ham, I’ve always thought of Dayton as the Mecca of ham radio. Younger and newer hams probably don’t feel that way. I’d bet some are thinking, “Dayton? Are they kidding”?

Another thing someone (the ARRL, perhaps?) might consider is somehow latching on to the Maker Faire. The people that attend the Maker Faire are exactly the kind of people that we want in ham radio, and I’d bet that a bunch of them would be inclined to become ham radio operators if given the chance. This is something I plan to look into.

Ham Radio: The Hobby of the Future

The U.K.’s Guardian reports on a study by British media regulator Ofcom that eventually everyone will be living in a wire-free world of sensors and high-tech car. The study, “Tomorrow’s Wireless World,” highlights several areas in health and transportation where wireless technology could have a significant impact.

The report suggests, for example, that body-area networks which monitor vital changes in the body and send a stream of information back to hospitals or doctors could transform the health care industry. In transportation, Ofcom predicts there will be widespread deployment of in-flight broadband services, as well as the use of new wireless technologies on trains, buses, and cars, including an intelligent transport system that will allow cars to communicate with each other to improve safety. “This technology is currently being developed by many of the major car manufacturers around the world and could be fitted to vehicles by 2015,” the report says.

The report also predicts that RFID technology and use will become increasingly complex. Many of the technologies in the report have already been deployed. Engineers at IBM have developed a system that uses the human body as a conduit for data, and General Motors is working with researchers at Carnegie Mellon University to develop a fully-automated car.

What does this have to do with ham radio? Everything, of course! Where do you think companies are going to get the engineers and technicians they’re going to need to design and produce these products? Ham radio operators are perfect in these positions. By indulging in a very enjoyable hobby, ham radio operators can prepare for the technology of the future.

Dayton 2008!

Well, I got back from three days at the Dayton Hamvention last night, and as usual, it was a real blast.

As I did two years ago, I started this year’s event with QRP-Amateur Radio Club International‘s Four Days in May seminars. This series of seminars lasts from 8:30 until about 4:00 pm and are just chock full of information and inspiration.

This year, the three presentations that really inspired me included:

  • “Life is Too Short for QR” by George Dobbs, G3RJV,
  • “QRP Contesting” by Ward Silver, N0AX, and
  • “Phasing Techniques in the Digital Age” by Phil Harman, VK6APH.

As you might expect, Rev. Dobbs’ talk was more inspirational than informational (please forgive the made-up word there). The thesis was that ham radio is a hobby, and we should indulge in it as such. That being the case, QRP is the perfect pursuit for those of us who treat it as a pastime.

It wasn’t all philosophy, though. Intertwined with the inspiration, George managed to sneak in a bunch of radio theory and simple circuits.

Just Do It
I do a bit of contesting—even a QRP contest now and then—so much of the material in Ward Silver’s talk was not news to me, but even so, it was both inspirational and informational. While he mostly exhorted the boys to just get out there and do it, he also included some pearls of wisdom.

One of the things he said that got me thinking was his explanation of how to use the two VFOs in your radio (assuming you’re using a radio with two VFOs) to maximize your “search and pounce” efforts. Basically, the technique goes something like this:

  1. Find a station calling CQ.
  2. Program your B VFO with that frequency.
  3. Find another station calling CQ.
  4. Switch back and forth between them until one of them answers your call.

This is a simple technique that ought to increase your score in the next big contest.

Phasing Techniques
Put this presentation squarely in the informational category. Phil explained phasing techniques and how software-defined radios use them so simply that even I understand it now.

Also, chalk this up as inspirational, though. While discussing the talk the next day with one of my colleagues who has been entranced by the SoftRock, we started considering how we might build some hardware of our own up and playing with it. We even went out an bought some cheap mixers from the Mini-Circuits booth to play around with.

Well, there’s just a quick take on my first eight hours in Dayton this year. More to come on the rest of the experience.

CO Museum Station to Hold Special Event

I don’t usually mention special event stations—unless it’s one I’m operating—but since this one is from a museum station, I thought I’d give them a plug……..Dan

The HF and 2-meter Amateur Radio station at Colorado’s Wings Over the Rockies Air & Space Museum is operational, and we just got approval to operate a special event station celebrating the astronaut and NASA festivities on Friday, May 23. We will have a 12-hour special event station operating on 14250 or 7250 kHz (+/-) from 0900 to 2100 Denver time (1500 UTC 23 May to 0300 UTC 24 May). We will provide an 8-1/2 x 11 QSL certificate to confirmed contacts for an SASE.

In addition to opening the new exhibit, “Colorado’s Astronauts: in their own words,” the museum will host ceremonies for the presentation of NASA’s “Ambassador of Exploration Award” honoring one of Colorado’s astronauts, Jack Swigert.

NASA officials will present the award, including a lunar sample (part of the 842 pounds of Moon rocks returned during the lunar expeditions from 1969 to 1972) which will be accepted by his sister, Virginia Swigert and placed on display at the Wings Over the Rockies Air & Space Museum.

In addition to NASA officials and Virginia Swigert, special guests include:
- Jeaneen Spinelli (Jack’s niece),
- other Swigert family members,
- General Hall (Jack’s Commanding Officer),
- Gene Kranz (Lead Flight Director, Apollo 13),
- James A. Lovell (Spacecraft Commander, Apollo 13),
- Fred Haise (Lunar Module Pilot, Apollo 13),
- Ken Mattingly (Original Command Module Pilot, Apollo 13),
- Jeff Ashby (NASA Astronaut),
- Richard Truly (NASA Astronaut), and
- additional Colorado astronauts.

Local officials include Colorado Governor Bill Ritter, other Colorado Elected Officials, and Colorado Space Industry Representatives.

We have been making progress in setting up our satellite radio system in our full-sized Space Station crew module exhibit. I hope it will also be operational in time to have a role in these activities.

Other information can be found via the links on the K0WAR QRZ.Com page.

Second One-Day Tech Class a Success

We held our second One-Day Tech Class yesterday, and I think I can claim success. Twelve folks signed up for the class, and eleven of them passed. This included current member Lisa Manthey and Candy Justyna, XYL of Ig, N0EFT.

Quite a few of the folks that passed learned about it via our local SkyWarn training. One of our club members took flyers with him when he went for the training, and about 20 folks expressed an interest there. About ten of them actually attended the class. I think it’s great that we were finally able to make that connection.

This time, I stressed pre-study, and I think it really paid off. The students seemed more prepared than they were last summer. Some students were so prepared that they decided to bolt after our first break and return at 3pm for the test. All three who did bolt, did indeed return and passed the test.

Onward and Upward
What I’m thinking about doing is to hold these at regularly-scheduled intervals, say ever two or three months. There were several SkyWarn people that expressed interest in the class, but could not make it yesterday. I also think that with more publicity, a regularly-scheduled class would make it easier for others to work this in to their schedules.

I’m also thinking a modest charge might be in order, say $10. Of course, all proceeds–except for perhaps a small amount used to purchase pizza for lunch–would be donated to our club. If 12 people attended each session, five sessions would net us about $500.

J-Pole Analyzed

On qrp-l.org, there’s been a discussion of the J-Pole antenna. There were various short, incomplete explanations of how it works, some comparing it to a Zepp antenna. I can see the similarity to a Zepp, but must also admit that my understanding of how it works is incomplete.

Fortunately, Gary, N3GO, has done a very thorough analysis of the J-pole titled “From a J to a Zepp: The truth and its consequences.” While I haven’t puzzled through it all yet, it looks like a very thorough analysis, and includes a number of observations that the author says appear to be contrary to popular opinion:

  • Adjusting the feedpoint “tap” is not the proper way to tune a J-pole.
  • 300 ohms is the optimal transmission line impedance to use in the construction of J-poles.
  • 300 ohm TV twin-lead is minimally susceptible to RF current induced in the feedline coaxial cable, enabling the J-pole to perform well without a balun.
  • The “stub” portion of the J-pole is electrically longer than a quarter wavelength.
  • The J-pole “shorting bar” can be connected to an earth ground reference if and only if a balun is employed at the antenna feedpoint.
  • The velocity factor is the most critical transmission line parameter to consider when designing J-poles.
  • J-poles are easy to build, and tune (even by the inexperienced). As a consequence, they are easy to reproduce.